Madbouyz, thank you for the reply....and yes, I meant flushing "muffs".

I agree, if there was a problem with water transfer grommet in the transome plate, I should have seen water running in when water pressure hits the area. The fact that it does not leak until I start the engine is suggesting to me the water pressure gets as far as the raw water pump, but not past it when the engine is off. When I start the engine, I'm now pushing water through the entire system. I did have the engine out a month ago and visually inspected the "Y-pipe" and there were no holes corroded through it that I could see. This has me thinking the problem might be the O-ring where the Y-pipe mounts down at the transome.

My best bet as far as I can determine would be to get a visual on the problem area, probably by using a borescope or similar. I've tried with an inspection mirror and just cannot get a good angle to really see the area closely.

It sounds like the Y-Pipe when the water is returning or the pressure drawing from the system is enough to expose the leak. One or the other

That's about where I am.....I've heard the O-ring at the Y-pipe joint can fail. Will let you all know what I find when I can dig into it.....thanks.

I had a similar leak and it was the o ring in the Y pipe. I think age and if it was ever overheated causes it to fail.

Donzi1979, thanks for the input. I am the sole owner of the boat and I'm confident it has not been overheated. The engine is a 7.4L, so we are not talking super high performance. The Bravo 1 should be a conservative outdrive for the 330 HP engine. The engine has rarely ever seen redline and I typically cruise at 2,700 to no more than 3,300 RPM. But age is another thing, 28 years. The O-rings on the outdrive were pretty stiff around the raw water inlet and lower drive unit oil connection, so it makes sense the O-ring to the Y-pipe could be the problem. For all I know the Y-pipe at the junction may have an issue. I'll have to take it apart to see what I find. Thanks for the input, this feedback is all helping me to point/head me in what I hope is in the right direction.